Process of pickling iron and steel.



A. F. HOFFMAN.

PROCESS OF PICKLING IRON AND STEEL.

APPLICATION FILED OCT- 17, 1914.

l 9 MM? 1 a Pafenfied July 13, 1915.

PJQV g ADDISON I. HOFFMAN, OF PITTSBURGH, PENNSYLVANIA.

PROCESS 01E PIGKLING IRON AND STEEL.

Specification of Letters Patent.

Patented July 13, 1915..

Application filed October 17, 1914. Serial No. 867,217.

To all whom it may concern:

Be it known that I, ADDISON F. HOFFMAN, a citizen of the United States,residing at Pittsburgh, in the county of Allegheny and State ofPennsylvania, have invented new and useful Improvements in the Processof Pickling Iron and Steel, of which the following is a specification.

My present invention relates to new and useful improvements in the'artof pickling iron and steel articles, and has for its especial objects,the handling and regeneration of the waste pickle liquor, in such amanner that this can be used over and over again, substantially withoutloss, except such losses as are due to leakage and the losses incidentto handling.

It is the usual practice to pickle iron or steel articles by immersingthem in a bath of dilute sulfuric acid, in order to remove scale,

rust and the like, the strength of the acid generally used being fromtwo and a half to fifteen per cent. and about four to eight per cent.being the average strength.

lVhen the acidity of the solution has fallen to about two per cent. orless, the waste liquor is ordinarily thrown away, although it haspreviously been proposed to recover iron sulfate crystals, pigments andthe like, from this waste liquor.

In operating in accordance with my proc ess, when the strength of thepickle liquor dropped to about one-half to two per cent. freeaS'LllfllliC acid, I draw off this waste pickle liquor into a suitablesettling tank and allow the same to stand for some time, in order tosettle, as completely as possible. The supernatant liquid is then drawn05. Instead of settling, I may pass the liquid through a suitable filterof similar device, to remove suspended solids. The liquid is thenaerated by allowing the same to trickle downwardly through a tower, inwhich coke, pebbles, bafiie plates orthe like are inclosed, in order tooxidize the major portion of its content of ferrous sulfate to ferricsulfate,

air being admitted to said tower at the bottom. In passing the liquiddownwardly through this device, no alkali or neutralizing agent whateveris to be added to the liquid. About 95% of the iron will readily beoxidized from ferrous sulfate to ferric sulfate, by passing through sucha device one or more times.

The liquid after aeration is heated to boil I ing, in an open or closedtank, which step basic ferric compounds and the consequent liberation ofa considerable amount of free acid. The liquid is then filtered ordecanted while hot, in order to se arate the free acid from theprecipitate 0 basic ferric compounds. The liquid may if desired betreated with a small amount of sulfuric acid, after filtration ordecantation, in order to bring up the strength to the desired degree ofacidity. The liquid may then be allowed to cool more or less, and isthen ready for use in pickling iron articles.

The precipitate obtained during the boiling operation appears to consistprincipally of basic ferric sulfate, with perhaps a small amount ofnormal ferric sulfate, and other .ferric compounds, and may becalcinedor heated in a mufiie, to a temperature of about 1100 F., atwhich tem erature it is converted into ferric oxid rouge suitable foruse as a pigment or polishing powder) and S0,. The latter may beabsorbed, to regenerate sulfuric acid for addition to the bath. In thismanner I can continue the use of the same pickle liquor with frequentregenerations, almost indefinitely the only loss being the small amountof loss due to leakage and handling, and I also am able to secure avaluable by-product in the form of the ferric oxid produced.

The step of heating the precipitated ferric compounds to produce freesulfuric acid and ferric oXid, may under certain condi t ons be omittedif the boiling has been car'- ried on to such an extent, that the liquidfrom this step contains sufiicient free acid, to again be economicallyused in pickling. Also this step of heating the precipitate may beomitted entirely, and sulfuric acid from an outside source used forbringing up the acidity of the pickling solution. The step of heatingthe precipitated ferric compounds may be also carried on independently'of the use of the sulfuric acid thereby formed, in pickling, for exampleWhere the precipitate is sold or shipped to another plant, for carryingout this operation. However, I prefer to carry out this step incombination with the pickling and regeneration of the pickle liquor, forthe reason that in employed, although the sulfuric acid produced by thisheating operation is a pure and concentrated acid, suitable for use asuse for pickling iron or steel, but on the con trary they improve itsvalue for this purpose, since the hydrogen liberated by the picklingoperation acts upon the ferric sulfate contained in the pickle liquor,to convert the same into ferroussulfate with the liberation of anadditional quantity of sulfuric acid. It also appears probable thattheferric sulfate itself, in the presence of an acid will act upon iron,to form ferrous sulfate, thereby aiding the pickling operation.

The accompanying drawing shows, diagrammatically, the complete apparatusused in the process of pickling the ferrous articles, and regeneratingthe pickle liquor.

In said drawing, the waste pickle liquor from the pickling vat may beconveyed to a settling vat, in which the solid material carried insuspension is allowed to settle. The clear liquor is then pumped intothe upper part of the aerating tower, air being blown in at the bottomof said tower. This step is performed at substantiallyatmospherictemperature. From the bottom of the aerating tower, theliquor is conveyed to the heating vat in which it is heated, for exampleby means of steam coils, thus causing the precipitation of basic ferriccompounds. After settling the clear liquor is allowed to flow to themixing vat, the precipitate being drawn off to asuitable calciningapparatusin which it is calcined, the acid thus produced .being added,if desired to the liquid in the tower, this pump may be placed at anyother part of the system, or pumps may be placed 1n several of thepipes, if desired.

articles the improvement which comprises pickling the same in a bath ofdilute acid, separating the Waste pickle liquor from the ferrousarticles, aerating the waste liquor, heating the same sufficiently tocause a precipitation of ferric compounds and a regeneration of freeacid, separating the precipitate from the liquor and thereafter treatingferrous articles with this regenerated liquor.

2 A cyclical process of pickling ferrous itltlOlQS, which comprisespickling said articles in a bath containing sulfuric acid, separatingthe waste pickle liquor from the ferrous art1cles, separating the solidsin suspension from said liquor, aerating said liquor at ordinarytemperature, heating said aerated liquor to boiling, to cause aprecipitation of basic ferric compounds, separating said basic ferriccompounds from said hot liquor, adding free acid to said liquor, andagain pickling iron articles therein.

3. A cyclical process of pickling ferrous metal articles which comprisespickling ferrous articles in a bath of dilute sulfuric acid, separatingthe waste pickle liquor from the articles being treated, aerating saidpickle liquor at ordinary temperature, heating said aerated liquorsufficiently to cause a precipitation of ferric compounds therefrom,separating said precipitate from said liquor, heating said ferriccompounds to generate free sulfuric acid, adding sulfuric acid to saidliquor from which precipitated ferric compounds have been removed, andpickling ferrous metal articles in the regenerated pickle liquor.

4. In the pickling of ferrous metal articles, the step of regeneratingthe waste pickle liquor which comprises aerating the waste pickle liquorat ordinary temperature, heating the aerated liquor sufficiently tocause a precipitation of ferric compounds therefrom, separating the.precipitate from the liquor, heating the precipitate sufliciently todrive off its content of acid and adding acid to the liquor from whichthe precipitate has been removed.

In testimony whereof I afiix my signature in presence of two witnesses.

ADDISON F. HOFFMAN.

